Pipeline leak detection system

Abstract: A system for detecting leaks in a pipeline (30) includes an outer containment pipe or jacket (32) surrounding a pipe and defining an interstitial space (34) therewith. A plurality of zone fittings (40) are disposed within the containment pipe or jacket to divide the interstitial space into a plurality of zones. An individual external sensor (60) is attached to the containment jacket at each of the zones for detecting the presence of fluid leakage into the interstitial space. The sensors generate an output signal which is operatively connected to visual and/or audible alarms (L1-L10, 38).

Description: The present invention relates to fluid storage and transfer facilities and, more particularly, to systems for detecting pipeline leakage. A typical storage facility may include a filling station, one or more storage tanks, a pump and a pipeline for conveying fluid from the tank to a discharge or outlet point in a plant or the like. In many applications, the pipeline may include under ground and above ground portions. For safety and environmental reasons, it may be important to control leakage from a pipeline system and to prevent ground water contamination into the system. Leakage detection systems have heretofore been proposed. These systems may rely upon visual inspection, the measurement of flow rates and the like to determine if leakage from the pipeline is occurring. In one method, as described in US-A-4 206 402 entitled SYSTEM AND METHOD FOR DETECTING LEAKAGE IN A PIPELINE OR TANK, which issued on June 3, 1980 to Ishido, a sensing coaxial cable is buried adjacent the pipeline or tank. The cable includes an outer conductor divided into a plurality of sections and a continuous inner conductor. The cable is fabricated from a material which prevents water from penetrating therethrough but which permits the penetration of a petroleum product. Leakage is detected by sensing the change in the dielectric constant of the coaxial cable when the cable is penetrated with a petroleum product. A system of this type will not detect ground water penetration into the pipeline. In order to contain the fluid being stored and conveyed, many facilities employ containment jackets or outer containment pipes which surround the main pipeline, Available leakage detection systems as for example described in DE-A-2 202 826 require penetration of the containment jacket. This, of course, may have an adverse effect on the integrity of the containment system. A need exists for a leak detection system which provides for fluid containment, which detects leakage from a main pipeline into a containment system and which does not require penetration of the containment system. According to the present invention there is provided a system for deleting leaks in a liquid pipeline, the system having the features of claim 1. Preferably, the system includes divider means between said main pipe and said containment pipe for dividing said interstitial space into a plurality of separately identifiable zones and includes a plurality of said sensors each sensor being associated with one of said zones and each sensor being operably connected to said alarm means. The sensors are preferably of a construction to detect ground water contamination in the interstitial space as well as and distinct from detection of leakage from the pipeline. In the preferred construction, the external sensors generate an output signal in response to the presence of a fluid which is to be detected within the interstitial zone and the output signal activates a visual alarm and an audible alarm. In one form, the external sensor is an adjustable capacitive proximity switch. Adjustment may be provided for detection of different fluids. Systems constructed in accordance with the present invention may be readily adapted to use with containment systems. The containment system is not penetrated. The system is adapted to above ground and under ground installations. The invention may be carried into practice in various ways but a number of systems constructed in accordance with the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic view of a liquid storage facility incorporating a detection system in accordance with the present invention; Fig. 2 is an elevational view of a portion of a containment system in accordance with the present invention; Fig. 3 is an elevational view of an above ground detection system in accordance with the present invention; Fig. 4 is a side, elevational view of a sensor assembly incorporated in the present invention; Fig. 5 is an end, elevational view of the assembly of Fig. 4; Fig. 6 is an end, elevational view of an alternative detection subassembly; Fig. 7 is a side, elevational view of a portion of a pipeline system incorporating a well; Fig. 8 is an elevational view of another portion of a pipeline system also incorporating a well; Fig. 9 is an elevational view of an under ground portion of a detection system in accordance with the present invention; Fig. 10 is an electrical schematic of a sensor and alarm system; and Fig. 11 is an elevational view of an alarm panel. A fluid storage facility system 10 illustrated in Fig. 1 includes a filling station 12 and a tank farm 14 including a plurality of individual storage tanks 16. The fluid stored in tanks 16 is delivered thereto by individual pipelines 18. Fluid is conveyed from tanks 16 to a plant or other use facility 20 by a plurality of individual delivery pipelines 22. In the preferred form, each individual pipeline 18, 22 is a double wall system including a main pipe 30 and an outer containment jacket or pipe 32. Pipe 32 surrounds pipe 30 and defines an interstitial space 34 therewith. Any leakage from main pipeline 30 is contained within the interstitial space 34 defined by the outer containment pipe or jacket 32. Similarly, ground water penetration into the pipeline 30 is prevented by the containment jacket. The containment system prevents ground water contamination caused by pipeline leakage. The interstitial space 34 is divided into a plurality of separately identifiable zones by zone fittings or dividers 40. Each zone fitting 40 includes an annular ring or spacer 42. The ring has an outer diameter which conforms generally to the inner diameter of the containment pipe 32. Each spacer 42 further defines a central bore or opening 44 having a diameter corresponding generally to the outer diameter of the inner pipe 30. Resilient gaskets or seals 46, 48 are positioned on the outer faces of rings 42 by suitable fasteners 50. As shown, inner pipe 30 is supported by spacers 42. When the zone fittings 40 are positioned, the fasteners are used to deform the seals 46, 48 into sealing engagement with the inner surface of outer containment pipe 32 and the outer surface of inner pipe 30. The outer containment pipe 32 is also divided into a plurality of separate sections for assembly purposes. In one form, outer pipe 32 is fabricated from a plastic material, such as a polyvinyl chloride (PVC). These sections are joined together by suitable solvents or adhesives in a known manner. Fittings 40 divide the pipeline into a plurality of defined and identifiable zones or sections. The zones permit the source or the location of leakage to be identified more easily. Fig. 3 illustrates a section of pipeline 22 which is above grade and suspended from a suitable structure by a pipe hanger 52. Hanger 52 includes a rod 54 and a pipe saddle or clamp 56. Zone fittings 40 divide the section or length of pipeline 22 into a single zone. An external sensor subassembly 60 is attached to the horizontal run of pipeline 22 between zone fittings 40. Sensor subassembly 60, as shown on Figs. 4 and 5, includes an attachment bracket 62 having a saddle-shaped portion 64 and a boss 66. A sensor 68 is threadably or otherwise suitably attached to a through bore defined by boss 66. Sensor 68 includes a power supply and output wire bundle 69. Bracket 62 may be fabricated from a suitable plastic material such as PVC. As shown in Fig. 3, saddle 64 is positioned on and, hence, partially surrounds the outer containment pipe 32. The saddle may be attached to the pipe by suitable solvents, adhesives or by clamps. Should leakage occur within the zone defined by fittings 40, as shown in Fig. 3, sensor 68 of sensor subassembly 60 will detect the presence of the fluid and generate an output signal. One possible form of sensor 68 is a capacitive proximity switch. Capacitive proximity switches or sensors are commercially available which will sense most materials including nonmetallics. Fluid detection or sensing is performed by a circuit containing an oscillator, a detector stage and an output stage. It is preferred that the capacitive sensor be adjustable to adapt the proximity sensor to sense fluids of different dielectric constants. Although low levels of condensation generally will not have an effect on sensor operation, it is recommended that the interstitial space be purged with clean, dry nitrogen. This will eliminate false alarms caused by condensate and also prevent oxidation of surfaces of the interstitial space. A commercially available capacitive sensor or proximity switch useable in the system described is available from BAUMER and sold under the model designation No. CFRK 30L24.32. Capacitive sensors detect the presence of unwanted fluids within the interstitial space by measuring the change in capacitance. The amount of change in capacitance depends upon the dielectric constant of the liquid being sensed. The larger the dielectric constant, the easier it is to detect the liquid. Liquids with high dielectric constants can be easily detected through the walls of containers made of a material with a lower constant. For example, water having a dielectric constant of 80 is readily detected through the wall of a PVC containment pipe which has a dielectric constant of 2.8. A petroleum product such as gasoline has a dielectric constant of 2.2, which is less than that of a PVC containment pipe. Larger quantities of such petroleum products need to be present before an output signal is generated than with aqueous solutions. The particular type of sensor selected, therefore, depends upon the sensitivity desired and the nature of the fluid to be detected. An alternative form of the sensor subassembly 60 is illustrated in Fig. 6 and generally designated by the numeral 72. Subassembly 72 includes a resilient, saddle-shaped portion 74 and a boss 76 for receiving a sensor element 78. Saddle-shaped portion 74 extends beyond 180 degrees in circumference. The saddle-shaped portion may snap-fit or clip on to the outer containment pipe 32. The subassembly 72 is, therefore, readily attachable to the pipeline system. Figs. 7 and 8 illustrate above ground portions of a pipeline system which incorporate detection wells 80 wherein fluid entering the interstitial space may collect. Fig. 7 shows a horizontal run, and Fig. 8 shows a run with a vertical riser section. As shown, a T-fitting 82 is joined to the individual section of containment pipe 32. A clear pipe section or segment 84 is joined to the T-fitting 82. A cap 86 is joined to the clear section 84. A drain valve 88 is attached to the cap. Well 80 will collect liquid from the interstitial zone. The presence of the liquid may be determined by visual inspection through the clear section 84. In addition, a sensor subassembly 60 is attached to well 80 at cap 86. Fig. 9 illustrates an under ground or below grade portion of a pipeline system. The system includes an outer containment pipe 32 surrounding the main pipe 30. A drip leg subassembly 92 is joined to the containment pipe 32 at a T-fitting 94. Drip leg 92 is generally L-shaped including a vertical leg 96 and a horizontal leg or run 98. Another T-fitting 102 is joined to horizontal portion 98. A riser pipe 104 extends from T-fitting 102 to a point above ground. The upper open end of riser 104 is closed by a clean-out plug 106. A clean-out 108 and a drain valve 109 are connected to T-fitting 102. An inner pipe having sections 110, 112 is positioned within the drip leg sections 96, 98. As a result, fluid entering the interstitial space between outer containment pipe 32 and inner pipe 30 will drain into the inner pipe sections 110, 112. A sensor subassembly 60 is attached to a lower end of an elongated sensor extractor 114. Extractor 114 permits placement and removal of sensor subassembly 60 upon removal of the clean-out plug 106 from riser 104. The drip leg 92 is also double contained as is the main pipeline. Fluid draining into the inner pipe sections 110, 112 will intersect the path of sensor 60 which, in turn, will generate an output signal. Fig. 10 illustrates an indicator, alarm or output system which is electrically connected to each of the sensors 68. In the system illustrated in Fig. 10, the pipeline is divided into ten separate interstitial zones, and ten sensors are provided. A regulated power supply 122 provides DC output. Power supply 122 is connected to each of the sensors by hot and common wires 124, 126. Output wires 128 from each sensor 68 are connected to a panel input 130. Each of the output wires 128 is connected to an output or a detection indicator panel of an enclosure 132 (Figure 11) . Enclosure 132 mounts visual indicators or lights designated L1-L10, which correspond to each of the zones 1-10. The electrical system further includes electrical relays 134, test switches SW1-SW10, a main switch MSW, an alarm relay 136 and an audible indicator, such as a horn, 138. Power is supplied to the lights and relays through wires 140, 142, 144, 146. As should be apparent from Figs. 10 and 11, when a zone sensor 68 senses the presence of a fluid in its interstitial zone, the output signal will actuate its respective relay 134 causing power to be supplied to the respective light indicator L1-L10. In addition, the audible alarm relay 136 will activate the alarm or horn 138. Since the system is divided into a plurality of zones, the location of the leak will be readily detected. The proximity switch or sensor will detect leakage from pipe 30 into the interstitial zone defined by containment pipe 32. In addition, ground water contamination or leakage into the containment system from the exterior thereof will also be detected. Visual detection is provided by the wells. The drip legs, which permit fluid to collect for sensing purposes, are also double contained to prevent or limit environmental harm. In accordance with the present invention, leakage detection is provided without penetration of containment pipes or jackets. Leakage location is easily determined. The system is readily adapted to under ground and above ground installations. In view of the foregoing description, those of ordinary skill in the art may envision various modifications which would not depart from the inventive concepts disclosed herein. Sensors other than capacitive proximity switches could be used depending upon the type of fluid or other material which is to be sensed and desired sensitivity. For example, inductive sensors which employ a coil and ferrite core assembly, an oscillator, a converter/trigger circuit and an output device may be used. It is expressly intended, therefore, that the above description should be considered as only that of the preferred embodiments, and that the scope of the invention is determined by the appended claims as interpreted under Patent law.

Claims: A system for detecting leaks in a liquid pipeline comprising: an outer containment pipe (32) surrounding a liquid pipeline (30) and defining an interstitial space (34) therewith; a sensor (60) applied to said containment pipe and responsive to a change of material within said containment pipe adjacent said sensor in order to produce an output; and output means (L1 - L10) responsive to a change in said output in order to produce an indication of the presence of a liquid in said containment pipe; characterised in that the sensor (60) is applied externally to the containment pipe and does not penetrate the containment pipe. A system according to claim 1 which includes divider means between said pipeline and said containment pipe for dividing said interstitial space into a plurality of separately identifiable zones. A system according to claim 2 which includes a plurality of said sensors, each sensor being associated with one of said zones and each sensor being operably connected to said output means. A system according to claim 1 in which said interstitial space (34) is divided into a plurality of zones by a plurality of dividers (42,46) disposed within the containment pipe (32), and in which each zone has a said sensor attached externally to said containment pipe for detecting the presence of a fluid contained within said pipeline which has leaked into the interstitial space (34) of said zone, and output means (L1-L10) operably connected to said sensor (60) for providing an indication of the detection of a leak by any one of said sensors. A system according to claim 4 which includes a well (80) joined to said containment pipe within one of said zones, one of said sensors (60) being attached to said well. A system according to claim 5 wherein said well is fabricated from a clear section of pipe permitting a visual inspection. A system according to claim 5 or claim 6 in which the well includes a pipe segment (84), a cap (86) joined to the segment and a drain valve (88) joined to the cap. A system according to any of claims 4 to 7 which includes a drip leg (92) joined to said containment pipe (32), an inner pipe (110,112) disposed within said drip leg and connecting with said interstitial space (34) so that fluid within said space will drain into said inner pipe, a riser (104) joined to said drip leg at a lower end thereof, and a sensor extraction member (114) disposed within said riser, one of said sensors (60) being connected to said extraction member, said one of said sensors being positioned on said inner pipe (112) for detecting the presence of fluid in said inner pipe. A system according to any of claims 4 to 8 in which at least one of said sensors (60) comprises an adjustable capacitive proximity switch, said switch generating an output signal when the fluid to be detected leaks into said interstitial space. A system according to any of claims 4 to 9 in which at least one of said sensors (60) comprises a saddle-shaped attachment bracket (62) configured to partially surround said containment pipe (32). A system according to any of claims 4 to 10 in which the output means comprises a power supply (122) connected to said sensors (60), a plurality of relays (134) operatively connected to said sensors and said power supply, visual indicators (L1-L10) operatively connected to said relays, and an audible indicator (138) operatively connected to said relays, each of said visual indicators being associated with one of said zones. A system according to any of claims 4 to 11 in which said dividers each includes a ring (42) having an outer diameter substantially corresponding to the inner diameter of said outer containment pipe (32) and a centre aperture (44) dimensioned to receive said inner pipe (30). A system according to any one of the preceding claims in which the output means includes alarm means for generating an alarm.

Inventors: MCATAMNEY DENNIS E, MCATAMNEY, DENNIS E.
Applicants: NIBCO, NIBCO INC.
Application year: 1994
Main classification: G01M3
IPC codes: G01M3